NPC interaction design

Hello everyone!

I’m currently making a game where players are able to attack every type of NPC (Including the kind that talks to you and gives you quests), which are normally invincible in most games. However, I still want people to be able to interact with the npc while it is busy with something else to not hinder another player’s progression.

Currently the best way I thought of to deal with this is to create some sort of visual thing (perhaps a humanoid outline where the npc originally is/spawns) that the players can also interact with as if it’s the same npc.

What are your thoughts on this, and what would be the best way to solve this issue?